Launch Thunderbird Converter program (Go to Start -> Programs -> Thunderbird Converter -> Thunderbird Converter). Then you will have the following screen:

Then you need to select Thunderbird files so as to convert thunderbird emails. There are 2 options to select Thunderbird files:

• Select Thunderbird file(s) - By clicking Select Thunderbird file(s) button you can select one Thunderbird file at a time or you can select Thunderbird files one by one.
  
  
• Select Folder Having Thunderbird file(s) - By clicking Select Folder Having Thunderbird file(s) button you can select a folder having multiple thunderbird file(s). Its a time-saving option. First collect all Thunderbird files in one folder, then select that folder to convert Thunderbird emails in batch mode.
  
  Know how to locate Thunderbird Emails or Files ?
  

After selecting Thunderbird files, you will have following screen:

Then choose your saving option (PST, EML, MBOX).

Then click on Convert Button. After clicking on Converter button you will have following screen:

Select the location to save your converted emails (pst/eml/mbox files) and Click OK.

After completion of the above process, you will have PST/EML/MBOX files saved in the selected saving location.